a) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device with capacitors having dielectric oxide films of a perovskite crystal structure, and its manufacture method.
b) Description of the Related Art
One memory cell of a dynamic random access memory (DRAM) is made of one transistor and one capacitor. In order to give a sufficiently large capacitance with a small capacitor, it is preferable that a capacitor dielectric film has as high a dielectric constant as possible. If the dielectric film is made of ferroelectric substance, the polarizing state of the dielectric film can be memorized so that a non-volatile ferroelectric random access memory (FRAM) can be realized.
As high dielectric constant substance having a relative dielectric constant of 10 or higher, or more preferably 50 or higher, oxide having a perovskite crystal structure is known such as barium strontium titanate (BST) (BaSrTiO). As ferroelectric substance, oxides having a perovskite crystal structure are also known such as PZT (PbZrTiO) and SBT (SrBiTiO). A dielectric oxide film of a perovskite crystal structure can be formed by spin-on such as a sol-gel method, sputtering, chemical vapor deposition (CVD), and the like.
A dielectric oxide film of a perovskite crystal structure just after it is formed often takes an amorphous phase or an insufficient crystallinity, or has often insufficient oxygen compositions. In such cases, the dielectric oxide film just after the film formation cannot be used as a good dielectric oxide film unless it is processed further. It is necessary to anneal it in an oxidizing atmosphere.
Even if insufficient oxygen atoms are replenished and the film is recrystallized, the characteristics of dielectric oxide are often degraded if the film is thereafter exposed in a reducing atmosphere such as high temperature hydrogen. However, in the manufacture processes of a semiconductor device, many semiconductor films and insulating films are formed by using hydrogen containing gas. After a dielectric oxide film of a perovskite crystal structure is formed, if another film is formed using such hydrogen containing gas, the dielectric characteristics of the film may be degraded considerably.